In general, natural gas is supplied in the form of pipe-line natural gas (PNG) that is fed to a consumption place from a production place through a pipe line or in the form of liquefied natural gas (LNG) that is liquefied through a vessel when a production place and a consumption place are far from each other and, in this case, LNG is used directly as fuel of transportation such as a vessel, a bus, and an automobile as well as general uses of liquefied natural gas and, to this end, LNG is generally stored in a cylindrical pressure tank and is stored and used in a pressure tank installed in transportation.
A general cylindrical pressure tank is conveniently used in an automobile or the like due to high pressure-resistant performance and a small volume but, when a large amount of liquefied natural gas is required like in a vessel, a plurality of cylindrical pressure tanks needs to be installed and, in particular, when liquefied natural gas is also used as fuel of a vessel, more cylindrical pressure tanks need to be installed in the vessel and, thus, there is a problem in that a space occupied in the vessel is excessively increased due to an interval between the cylindrical pressure tanks when the plurality of cylindrical pressure tanks are arranged.
When a cylindrical pressure tank is installed in a bus and an automobile, an installation space is limited due to its shape, thereby degrading space utilization.
To overcome the problem, a membrane or circular tank system, but not a cylindrical tank system, has been developed and Korean Patent Publication No. 10-1254788 discloses a square pressure tank configured by improving defects of the membrane or circular tank system, like in FIG. 1 of the present application.
The square pressure tank advantageously and largely improves space efficiency, which is disadvantage of the conventional membrane or circular tank system, but it is required to overcome a problem in terms of its high weight.